1. Field of the Invention
This invention relates to polyurethane elastomers and is more particularly concerned with thermoplastic polyurethane elastomers derived from polyether polyols and with methods for their preparation.
2. Description of the Prior Art
The preparation of thermoplastic polyurethane elastomers from polyester polyols is well-known in the art. Such elastomers can be extruded, injection molded and fabricated in other known manner without suffering any degradation due to momentary exposure to the relatively high processing temperatures (of the order of 400.degree. F.) involved in such techniques. In contrast, it has not hitherto been possible to use polyethylene and polypropylene glycols to prepare thermoplastic polyurethanes, which can be molded by techniques involving processing temperatures of the above order. It is highly desirable that such polyurethanes be prepared since polyethylene and polypropylene glycols are significantly less expensive than polyester polyols and thereby would provide obvious economic advantages. The latter would be in addition to the recognized advantage in hydrolytic stability of the resulting polyurethanes, which hydrolytic stability is associated with the use of polyether polyols as opposed to polyester polyols.
Unfortunately it has been found hitherto that polyurethane elastomers prepared using polyether polyols, particularly polypropylene glycol, are not capable of withstanding exposure to temperatures of the order of 400.degree. F. even for a brief period such as that required in injection molding and like techniques.
We have now found that, by using a particular group of block copolymer polyether glycols which have not hitherto been regarded as potential candidates for polyols in the preparation of polyurethane elastomers, it is possible to prepare thermoplastic polyurethane elastomers which will withstand temporary exposure for limited periods to temperatures as high as 450.degree. F. These elastomers can be fabricated readily, without degradation, by extrusion, injection molding and the like. This finding results in marked advantages in terms of reduction in cost as well as the ability to use the more hydrolytically stable polyether based polyurethane elastomers for fabrication of articles by injection molding and the like.